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difference of viewport performance between a model with modifiers and modifiers applied
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Description

System Information
Operating system: Windows 7
Graphics card: Nvidia GTX 1060
Blender Version: 2.80 Beta
Hash: e4dbfe0a98c1
Date: 2018-12-26

Description:
-I have a vehicle model with different parts and modifiers.
-When i move the vehicle in the viewport (parented to a box) i get 2 o 3 FPS but if i applied all the modifiers i get 30 FPS despite having the same number of polygons.
-In Blender 2.79, i can move the model with modifiers without problem at 30 fps.

Exact steps for others to reproduce the error:
In the attached file you will see both models, one with modifiers and the other one with the modifiers applied. Move the different wire boxes to compare the fps rates. (the file is heavy although i erase some parts, because if i simplified even more, the problem start to disappearing).

Thanks.

Event Timeline

Sebastian Parborg (zeddb) triaged this task as Confirmed, Medium priority.

@Sergey Sharybin (sergey) I think this should be depsgraph related, right? (The finished result should be cached)

But I guess that the performance drop might be related to OpenSubDiv too as the evaluation is slower.

@Sebastian Parborg (zeddb), not sure what you mean by "cache" exactly. In Blender terms it is not supposed to be cached. Is "just" things which are not tagged for update are not supposed to be re-evaluated, and previous evaluation result will be used.

The actual issue here is that such modifier stack is not supposed to be re-evaluated when object transform changes. More slow nature of OpenSubdiv just made the actual issue more obvious.

The root of the issue is the Mirror modifier which says "i do depend on transform of the object", even though actual modifier evaluation does not depend on it unless mirror object is set.

Fix is coming in a bit.

P.S. Forgot to mention, the OpenSubdiv will "cache" topology, so its evaluation will become faster even in more tricky setup.